Reduce secondary pump head and ease secondary heating

src/reactor_sim/constants.py

@@ -24,7 +24,7 @@ MEV_TO_J = 1.602_176_634e-13
 ELECTRON_FISSION_CROSS_SECTION = 5e-16  # cm^2, tuned for simulation scale
 PUMP_SPOOL_TIME = 5.0  # seconds to reach commanded flow
 PRIMARY_PUMP_SHUTOFF_HEAD_MPA = 8.0  # approximate shutoff head for primary pumps
-SECONDARY_PUMP_SHUTOFF_HEAD_MPA = 7.0
+SECONDARY_PUMP_SHUTOFF_HEAD_MPA = 3.0
 TURBINE_SPOOL_TIME = 12.0  # seconds to reach steady output
 
 # Turbine/condenser parameters

src/reactor_sim/reactor.py

@@ -324,7 +324,7 @@ class Reactor:
                 pump_state.status = "STOPPING" if pump_state.flow_rate > 0.1 else "OFF"
         if self.secondary_pump_active:
             total_flow = 0.0
-            base_flow, base_head = self.secondary_pump.performance(0.75)
+            base_flow, base_head = self.secondary_pump.performance(0.5)
             target_pressure = max(0.5, base_head * power_ratio)
             loop_pressure = max(0.1, saturation_pressure(state.secondary_loop.temperature_out))
             target_flow = base_flow * power_ratio
@@ -428,8 +428,10 @@ class Reactor:
             )
             state.secondary_loop.temperature_in = state.secondary_loop.temperature_out
         else:
-            secondary_cooling = max(0.0, state.secondary_loop.temperature_out - env - 40.0)
+            # Allow the secondary to retain more heat so it can approach saturation and form steam.
-            state.secondary_loop.temperature_in = max(env, state.secondary_loop.temperature_out - max(20.0, secondary_cooling))
+            excess = max(0.0, state.secondary_loop.temperature_out - env)
+            cooling_drop = min(40.0, max(10.0, 0.2 * excess))
+            state.secondary_loop.temperature_in = max(env, state.secondary_loop.temperature_out - cooling_drop)
 
         state.primary_to_secondary_delta_t = max(0.0, state.primary_loop.temperature_out - state.secondary_loop.temperature_in)
         state.heat_exchanger_efficiency = 0.0 if total_power <= 0 else min(1.0, max(0.0, transferred / max(1e-6, total_power)))

src/reactor_sim/state.py

@@ -18,12 +18,17 @@ class CoreState:
     reactivity_margin: float  # delta rho
     power_output_mw: float  # MW thermal
     burnup: float  # fraction of fuel consumed
+    clad_temperature: float | None = None  # Kelvin
     xenon_inventory: float = 0.0
     iodine_inventory: float = 0.0
     delayed_precursors: list[float] = field(default_factory=list)
     fission_product_inventory: dict[str, float] = field(default_factory=dict)
     emitted_particles: dict[str, float] = field(default_factory=dict)
 
+    def __post_init__(self) -> None:
+        if self.clad_temperature is None:
+            self.clad_temperature = self.fuel_temperature
+
     def update_burnup(self, dt: float) -> None:
         produced_energy_mwh = self.power_output_mw * (dt / 3600.0)
         self.burnup = clamp(self.burnup + produced_energy_mwh * 1e-5, 0.0, 0.99)
@@ -111,6 +116,10 @@ class PlantState:
         core_blob = dict(data["core"])
         inventory = core_blob.pop("fission_product_inventory", {})
         particles = core_blob.pop("emitted_particles", {})
+        # Backwards/forwards compatibility for optional core fields.
+        core_blob.pop("dnb_margin", None)
+        core_blob.pop("subcooling_margin", None)
+        core_blob.setdefault("clad_temperature", core_blob.get("fuel_temperature", 295.0))
         turbines_blob = data.get("turbines")
         if turbines_blob is None:
             # Compatibility with previous single-turbine snapshots.